Devices to utilise the difference of velocity, or power, between two
distinct moving parts.
=547. Equational box.= Two drivers ~A~, ~A′~, equally speeded in
opposite directions, will drive the bevil gear at same velocity without
revolving the spur wheel ~C′~ which is loose on the shaft; but any
alteration in the relative speeds of ~A~ and ~A′~, causes the bevil
pinion to travel round, carrying the spur wheel ~C′~ at a speed equal to
half the difference of the two velocities. This gear is used on traction
engines to drive the swivelling wheels round curves, where the
proportionate velocities of the wheels will vary with the radius of the
curve. In this application of the gear ~B~ is the driving shaft, and ~A~
and ~A′~ the swivelling wheels.
=548. Is a modification of 547.= The pinion ~A~ may be controlled in
speed by any hand or automatic device, to vary the speed of the driven
pinion ~B~. The belt pulley ~C~ carries round the bevil wheel ~D~,
driving ~B~ at a speed varying with the motion given to ~A~.
=549. Two wheels= (one of which has a different number of teeth to the
other) gearing into one pinion; used for counters and slow motions of
all kinds.
=550. Is an application of No. 549= by internal or epicycloidal gear to
pulley blocks. Moore’s patent (No. 1545) and Pickering’s patent are
examples. The arm shown is not required where two internal _loose_
wheels are used with different numbers of teeth, and one pinion as in
No. 1545, but if used is fixed to the pinion so that it is prevented
from revolving, but retains its circular swaying motion; in this case,
one internal wheel is movable and the other fixed, the speed being equal
to the difference in number of teeth of the loose wheel and pinion at
each revolution of the eccentric shaft.
=551. Weston’s differential pulley block,= consisting of a two-grooved
pitched chain-sheave having different numbers of teeth, in combination
with a return block and endless chain.
=552. Differential screws.= These may be both of the same hand, or one
right and one left-handed, and any fractional speed secured by
proportioning the pitches.
[Illustration: 531.-552.]
=553. Two-speed gear,= operated by a double clutch, which throws either
pair into gear as required.
=554. Stewarts’ differential gear.= Two cranks, one fixed to a sleeve
and the other to a centre shaft, are driven round at varying velocities
by a slotted crosshead revolving with the driving shaft. The two shafts
are not in the same line.
=555. Differential hydraulic accumulator.= The effective area of the ram
is the annular shoulder, or the difference between the areas of the top
and the bottom rams.
=556. Differential governing device.= The motive power drives ~A~ which
winds up the large weight; the small weight tending to run down, drives
the fan regulator, and the two weights are so adjusted that when the
proper speed is attained, both weights are stationary; any change of
speed causes them to run up or down, so actuating the regulation by the
bell crank lever and rod.
=557. Varying differential regulator.= The upper rod ~A~ is connected to
the regulator valve or other device, and it is capable of receiving
motion from either the piston, which acts against a spring, or from the
rod ~B~ attached to some positive reciprocating part, so that the nett
movement of ~A~ is due to the difference of motion of ~B~ and the piston
~C~.
Differential Worm Gear, No. 1559.